In the construction of building structures prefabricated members, i.e., roof trusses and roof rafters, are used to support the roof decking. The distance between roof trusses and/or rafters is generally determined by measuring with a ruler and nailing wooden strips, 1 .times. 2 in. in cross section, to secure the members in place. Mistakes in measuring are common and time is lost in correcting the mistakes. Furthermore, after the trusses or rafters are fixed in the desired location the strips must be removed to permit the roof sheeting to be installed. The strips are frequently thrown away as scrap, resulting in the waste of expensive lumber.